The invention concerns multi-layer composite plates, and a process for producing multi-layer composite plates.
Multi-layer composite plates and process for production of multi-layer composite plates are broadly employed in lightweight construction materials.
Above all in the field of transportation, specific lightweight materials, such as aluminum or fiber reinforced composite materials, or even high strength automobile body steel, are preferably employed. However, while it may be possible to satisfy the strength requirements when employing materials of increasing strength and increasingly thinner sheet thicknesses, it is not possible therewith to satisfy the stiffness requirements. Lightweight materials encounter limitations above all there, where for geometric reasons the reduced cross-section is no longer sufficient to satisfy the requirements for the construction material stiffness. One solution is offered by geometric stiffening along with low surface area weight, the so called high specific stiffness. This type of multi-layer composite is already known in many variations such as web plate, dimpled, and trapezoid or pitch composite plates, in which geometry is produced by deforming or bending with internally supporting intermediate materials offering the basis for the technological solution in lightweight materials. As suitable intermediate materials, mentioned may be made of foam core fillers with polymeric foams or even metallic foams and even diatomaceous earth fillers.
Preferred industrially today is above all a three-layer material composite comprised of two steel sheets and an intermediate layer of visco-elastic material. This type of composite sheet material is employed on the basis of its relatively thin intermediate layer, which partly contributes towards increasing stiffness, but mainly contributes value by virtue of its oscillation dampening characteristics.
Besides this, there is known from DE 39 35 120 C2 a process for production of multi-layer composite plates, which are comprised of a top and a base plate and sandwiched in between is a cross-over material of wire, which is welded or adhered at the wire contact points of the mesh. Even though in certain cases, during the production process the intermediate layer, the lattice or mesh contact points or xe2x80x9cknotsxe2x80x9d are rolled flat, whereby a greater contact surface is offered to the top and base plates, nevertheless in particular the contact points far from the neutral plane can however be subjected to strong thrust forces and thereby rip. As soon as, during the deformation process, connecting points damaged in this way drift apart from each other even minimally, these are not subsequently reattached, even when using surface contacting adhesives in subsequent process steps. As a general rule, it can be said that with respect to deformability, the higher the so-called weight specific stiffness of a structure is, the narrower are the limits, out of which a planar composite structure can be deformed into a curved construction component. This applies in principle also for lattice and expanded metal composites, wherein due to the compressing of the intermediate material during deformation, the punching-through of the intermediate layer structure on the traverse sheets and even a ripping open of the cover sheets limits the degree of deformability.
In the more complex structures described in terms of the manufacturing process in document EP 0 636 517 B1, the individual layers and intermediate filler layers are joined into multi-layer composite plates with the aid of an adhesive and this composite is then deformed. The essence of the disclosure lies particularly in the targeted deformation of vehicle chassis parts, in which with partially applied welding or adhesive connections a desired deformation relationship is achieved, and therein only in second instance is the achievement of a high-as-possible stiffness desired or targeted. Further, also in this case the multi-layer composite plates exhibit the already mentioned disadvantages.
The invention is thus concerned with the task of providing a multi-layer composite plate suitable for further deforming, as well as a process for the production thereof, whereby in its material characteristics optimal stiffness is achieved, and this in combination with corrosion protection and vibration and sound dampening.
The invention comprises multi-layer composite plates, which include two outer metal sheets as top and base plates, and which are bonded by an intermediate deformable connecting material. Therein the top and base plates are preferably bonded to the connecting material by means of a foaming adhesive, which fills any voids remaining in the composite. The intermediate connecting material is preferably comprised of an expanded metal lattice or mesh or grate, a wire matrix, or a web plate. It could however also be built up of multiple layers of expanded metal lattice, wire mesh, and web plate with intermediate sheets of adhesive transmissive or adhesive non-transmissive materials.
The voids remaining in the composite are completely or partially filled by the foaming adhesive.
The process for production of multi-layer composite plates includes the step of introducing adhesive in between the lamina or plies to be adhered, and then subjecting the adhesive to a thermal treatment. The adhesive between the plies or layers may be in the form of a foil intermediate layer or in liquid form.
By the thermal treatment, the adhesive is completely or partially hardened. In the case of a partially hardened adhesive the adhesive is subjected to further thermal treatment and completely hardened only after the step of deformation of the multi-layer composite plate.
A particular advantage of the invention is comprised in the excellent deformability of the multi-layer composite structure. Within the workpiece the flowing tension transition insures supplemental advantageous material characteristics of the highly stiff structure formed by the deformation in conditions of use. In addition to this, due to the coverage of the internal metal surfaces by the foamed adhesive, an effective protection against corrosion results. A further advantage results from an improvement in the vibration and sound dampening characteristics and with respect to the thermal insulation.